1. Field of the Invention
This invention relates generally to the determination of various parameters in a subsurface formation penetrated by a wellbore, and, more particularly, to such determination after casing has been installed in the wellbore by way of communication across the wall of the casing with remote sensors deployed into the formation prior to the installation of the casing.
2. Description of the Related Art
Present day oil well operation and production involves continuous monitoring of various well parameters. One of the most critical parameters required to ensure steady production is reservoir pressure, also know as formation pressure. Continuous monitoring of parameters such as reservoir pressure indicate the formation pressure change over a period of time, and is necessary to predict the production capacity and lifetime of a subsurface formation. Typically, formation parameters, including pressure, are monitored with wireline formation testing tools, such as those tools described in U.S. Pat. Nos. 3,934,468; 4,860,581; 4,893,505; 4,936,139; and 5,622,223.
The '468 patent, assigned to Schlumberger Technology Corporation, the assignee of the present invention, describes an elongated tubular body that is disposed in an uncased wellbore to test a formation zone of interest. The tubular body has a sealing pad which is urged into sealing engagement with the wellbore at the formation zone by secondary well-engaging pads opposite the sealing pad and a series of hydraulic actuators. The body is equipped with a fluid admitting means, including a movable probe, that communicates with and obtains samples of formation fluids through a central opening in the sealing pad. Such fluid communication and sampling permits the collection of formation parameter data, including but not limited to formation pressure. The movable probe of the '468 patent is particularly adapted for testing formation zones exhibiting different and unknown competencies or stabilities.
The '581 and '139 patents, also assigned to the assignee of the present invention, disclose modular formation testing tools that provide numerous capabilites, including formation pressure measurement and sampling, in uncased wellbores. These patents describe tools that are capable of taking measurements and samples at multiple formation zones in a single trip of the tool.
The '505 patent, assigned to Western Atlas International, Inc., similarly discloses a formation testing tool capable of measuring the pressure and temperature of the formation penetrated by an uncased wellbore, as well as collecting fluid samples, at a plurality of formation zones.
The '223 patent, assigned to Halliburton Company, discloses another wireline formation testing tool for withdrawing a formation fluid from a zone of interest in an uncased wellbore. The tool utilizes an inflatable packer, and is said to be operable for determining in situ the type and the bubble point pressure of the fluid being withdrawn, and for selectively collecting fluid samples that are substantially free of mud filtrates.
Each of the aforementioned patents is limited in that the formation testing tools described therein are only capable of acquiring formation data as long as the tools are disposed in the wellbore and in physical contact with the formation zone of interest.
U.S. patent application Ser. No. 09/019,466, also assigned to the assignee of the present invention, describes a method and apparatus for deploying intelligent data sensors, such as pressure sensors, from a drill collar in the drill string into the subsurface formation beyond the wellbore while drilling operations are being performed. The positioning of such data sensors during the drilling phase of an oil well is accomplished by means of either shooting, drilling, hydraulically forcing, or otherwise deploying the sensors into the formation, as described in the '466 application which is incorporated by reference herein in its entirety.
The '466 application further discloses the use of means for identifying the location of such data sensors long after deployment, particularly through the use of gamma-ray pip-tags in the sensors. These gamma-ray pip-tags emit distinct radioactive "signatures" that are easily contrasted to the gamma-ray background profiles or signatures of the local respective subsurface formation, and thereby facilitate a determination of each sensor's location in the formation.
At some stage during the completion phase of the well, a string of casing will be installed in the wellbore. After the wellbore has been lined with casing and the casing has been cemented, if necessary, standard electromagnetic communication from inside the wellbore with the individual remote sensors outside the casing is no longer possible. If there is no effective means of communicating with a data sensor which has been embedded beyond the cased wellbore in the formation, the data sensor has no utility. Thus, for the remote data sensor(s) to provide continuous formation monitoring capabilities during the productive life of the wellbore, communication with the data sensors must be reestablished. Furthermore, for the communication with the data sensor(s) to be optimized, the location of the sensors must be identified after the wellbore has been cased and cemented.
The tools and methods described in the '468, '581, '139, '505, and '223 patents mentioned above are not intended for use in cased wellbores, and are generally not permanently connected to the wellbore or formation. However, formation testing tools and methods that are intended for use in cased wellbores are well known in the art, as exemplified by U.S. Pat. Nos. 5,065,619; 5,195,588; and 5,692,565.
The '619 patent, assigned to Halliburton Logging Services, Inc., discloses a means for testing the pressure of a formation behind casing in a wellbore that penetrates the formation. A "backup shoe" is hydraulically extended from one side of a wireline formation tester for contacting the casing wall, and a testing probe is hydraulically extended from the other side of the tester. The probe includes a surrounding seal ring which forms a seal against the casing wall opposite the backup shoe. A small shaped charge is positioned in the center of the seal ring for perforating the casing and surrounding cement layer, if present. Formation fluid flows through the perforation and seal ring into a flow line for delivery to a pressure sensor and a pair of fluid manipulating and sampling tanks.
The '588 patent, also assigned to the assignee of the present invention, improves upon the formation testers that perforate the casing to obtain access to the formation behind the casing by providing a means for plugging the casing perforation. More specifically, the '588 patent discloses a tool that is capable of plugging a perforation while the tool is still set at the position at which the perforation was made. Timely closing of the perforation(s) by plugging prevents the possibility of substantial loss of wellbore fluid into the formation and/or degradation of the formation. It also prevents the uncontrolled entry of formation fluids into the wellbore, which can be deleterious such as in the case of gas intrusion.
The '565 patent, also assigned to Schlumberger Technology Corporation, describes a further improved apparatus and method for sampling a formation behind a cased wellbore, in that the invention uses a flexible drilling shaft to create a more uniform casing perforation than with a shaped charge. The uniform perforation provides greater reliability that the casing will be properly plugged, because shaped charges result in non-uniform perforations that can be difficult to plug, often requiring both a solid plug and a non-solid sealant material. Thus, the uniform perforation provided by the flexible drilling shaft increases the reliability of using plugs to seal the casing. Once the casing perforations are plugged, however, there is no means of communicating with the formation without repeating the perforation process. Even then, such formation communication is possible only as long as the formation tester is set in the wellbore and the casing perforation remains open.
To address the problems and shortcomings of the related art, it is a principal object of the present invention to provide a method and apparatus for reestablishing communication with remotely deployed data sensors across the casing wall and cement layer of a cased wellbore.
It is a further object to provide a method and apparatus for determining the location of each such data sensor in the subsurface formation relative to the casing wall.
It is a further object to provide a method and apparatus for creating an opening in the casing wall and cement layer that line a cased wellbore proximate the location of a data sensor or group of data sensors.
It is a further object to provide a method and apparatus for installing an antenna in the created opening in sealed relation with the casing wall for communicating with the remote data sensor or sensors.
It is a still further object to provide a method and apparatus for transmitting command signals to the remote data sensors and receiving data signals from the remote data sensors via the installed antenna to monitor the wellbore.
It is a still further object to provide a data receiver that utilizes a microwave cavity and is positionable within the wellbore to communicate with the remote data sensor(s) via the installed antenna(s).